


three's a crowd.

by piecksz



Category: Shingeki no Kyojin | Attack on Titan
Genre: Cuckolding, Degradation, Explicit Language, Explicit Sexual Content, F/M, Implied/Referenced Drug Use, Light Angst, Masturbation, NSFW, Oral Sex, Vaginal Sex, Voyeurism
Language: English
Status: Completed
Published: 2021-02-23
Updated: 2021-02-23
Packaged: 2021-03-14 01:07:55
Rating: Not Rated
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,688
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29660118
Author URL: https://archiveofourown.org/users/piecksz/pseuds/piecksz
Summary: Reiner’s attempt at hiding his attraction towards you fails, but lucky for him, Eren’s feeling generous.
Relationships: Eren Yeager/Reader, Reiner Braun/Eren Yeager, Reiner Braun/Reader
Comments: 5
Kudos: 105





	three's a crowd.

Reiner hated Eren.

He hadn’t gone into living with someone he’d never met in person before with innumerable expectations, but he wasn’t banking on his roommate to be his polar opposite. He hated the sound of Eren’s riotous music into the early hours of dawn. He hated the unbearable malodor of his marijuana dependence, and he hated the way he carried himself with an intolerable air of arrogance, but as much as Eren’s living habits irritated him, it was the fact that Eren had you that presided over all of his grievances.

Being a witness to it made Reiner sick, knowing that you were leagues above Eren, and surely you deserved someone respectable, but somehow he’d charmed you into a long-term relationship, and Reiner wondered how he’d managed it. If by some miracle it had been up to him, Reiner speculated that _he_ would be a viable match for you--that was if he had those sentiments for you--and he reassured himself he didn’t hold any promiscuous feelings towards his roommate’s girlfriend.

Yet it was hard for Reiner to rationalize the obscene thoughts that pervaded his mind at 2 AM. His clock displayed the time in bold red numbers, an indication that he should have been fast asleep, but you had decided to spend the night, and he already understood what that entailed.

The walls in their apartment were thin and did an insubstantial job of muting the noise that traveled between rooms. Reiner boasted the privilege of having his room right next to Eren’s, which meant he could hear everything that happened on the other side of the barrier. He heard every whimper, every groan, every time Eren praised you for taking him so well, and every time he admired how irresistible you looked while he fucked you from the back. The sound was so lucid he could count exactly how many rounds you guys had gone, and it was usually two, three if Eren hadn’t seen you in a while which was rare.

You two were hard to ignore, no matter how hard Reiner had tried, meaning he was also up late, listening while you two coupled. Your cries of stimulation, however, he didn’t mind as much. In truth, Reiner was always tempted to slip his hands into his pants and get himself off to the sound of your enticing whimpers, but he would discourage himself, deciding it was against his better judgement. Instead he would opt to cover his ears with his pillow, flipping over onto his side and dedicating his total effort to falling asleep. 

Of course, Reiner had long established that he didn’t like you, but he swore he could make you feel better than Eren could.

* * *

It was around midday when Reiner returned to their apartment after committing his morning to helping his long-time friend, Pieck, pack up the furniture at her studio in preparation to move. They were halfway finished with stowing away Pieck’s belongings before she realized they didn’t have enough boxes and apologized, asking Reiner if he’d be willing to return the following day to help her load up her remaining things. He obliged, guiltily happy that he was being dismissed early.

Reiner kicked off his shoes and ambled into the kitchen to set down the food he secured on his way home, but he paused momentarily to scrutinize the condition of the living room, discerning Eren’s obvious trace.

The TV was on, but it sat idly, blinking images of some prime time movie Reiner couldn’t recognize, and Eren’s drug paraphernalia was left scattered on the coffee table, his bong alongside his stray lighter and grinder.

“Eren!” Reiner had prompted him on several occasions, reminding Eren that just because he thought electricity was a necessary utility and should be free, didn’t mean it was, they still had to pay for it. He also requested that he put his bong away after he was done smoking since it wasn’t permitted in their building, but Eren seemed heedless to that demand too. “ _Eren!_ ”

Reiner anticipated a response, but huffed when he received only silence. Leave it to his roommate to blight his good mood in record time. He mumbled inaudibly, swiping the remote off the table to turn the TV off, and then reluctantly bending down to tidy the space of Eren’s things.

“ _Hi, Sunshine. You’re up and about early_.”

Reiner straightened himself out and turned around, unaware that you’d been over. He missed your approaching footsteps. Had you stayed the night? He didn’t hear anything from Eren’s room the previous evening which was unusual to say the least. Maybe you’d stopped by earlier that morning while he’d been out.

“Hey,” he replied meekly. “Sorry, I didn’t know you were here.”

Reiner’s eyes looked you over swiftly, slightly startled at the lack of clothing covering your bottom half. You were only wearing a loose shirt that stopped dangerously at your hips and a pair of lace undergarments, but naturally, you didn’t seem the least bit phased. You’d practically lived with them. When you weren’t in class or at your part-time job, you were at their apartment, leading Reiner to wonder if you forgot you had a place of your own. 

“It’s fine,” you smiled. “Sorry Eren left all of his shit out. I don’t know how I know the house rules and he doesn’t.”

Reiner snorted. “He knows them, he just doesn’t care.” His voice was casual although he walked hastily into the kitchen to avoid looking at you. He stored Eren’s bong in the vacant cupboard above the microwave before throwing his other tools into a miscellaneous drawer.

As if on cue, Eren wandered out of his room languidly, carelessly shrugging a jacket onto his unclad upper body. Reiner took that as a sign that his lunch would be best enjoyed in his room. He was already irked, and wasn’t in the headspace to deal with the current atmosphere.

“What’d you get?” you questioned, leaning over the counter with mirth. You paid little attention to the way Eren came up behind you, circling his arms around your waist and resting his chin in the curve of your shoulder. You looked more interested in the alluring smells wafting from the paper bag in Reiner’s hand.

Another thing he hated about Eren was his shameless PDA. It appeared he adored showing you off, letting everyone know that you were his, but _God--_ how could anyone forget when it seemed he was incapable of keeping his hands off of you. Reiner himself recognized that you were a prize, from your lively eyes that were a marriage of subtle hues to the way your lips curled upwards when you grinned. He even noticed the curve of your breasts’ shape through your shirt. If Reiner had you, he’d want you all to himself.

He shook the thought out of his head.

“I just got something small on the way home.” He forced a smile. “If I’d known you were over I would have gotten you something too.”

“Why do you treat Y/N better than you treat me?” Eren asked, sounding only a little bit offended.

Reiner pretended to think before he responded. “Ah, maybe because I don’t like you.”

You laughed at Reiner’s reply, and Eren only smiled, but Reiner detected something else behind his expression. Mischief.

“Do you like Y/N?”

Reiner creased his eyebrows together. “Of course.” He hadn’t read too much into the question. He _did_ like you. You weren’t just easy on the eyes, but you were great company too. That was the only reason he didn’t mind lending their apartment to you as a second home, he enjoyed being around you.

You let out an exaggerated _aww_ after he answered. “I like you too, Reiner.”

Reiner chuckled, shaking his head, but inside he was telling his heart to calm down. You didn’t mean it like that.

Eren hummed absentmindedly, swaying side to side slowly while you rocked along to his movement.

“Do you wanna fuck her?”

Reiner gripped the bag in his hand tightly, and his smile faltered in shock, reeling from the bombshell of Eren’s question. “What?” Did he hear him correctly?

You looked just as surprised, exclaiming your boyfriend’s name and craning your neck to look at him.

“I’m _kidding_ ,” he dismissed, but Reiner could tell he wasn’t from the way Eren’s eyes didn’t waver from him.

What Reiner didn’t know was that Eren had caught onto him. He’d known for a while, which was why he was particularly touchy with you around Reiner, showing you off, not caring whether you walked around their apartment scarcely dressed, it was because Eren enjoyed having something that someone else wanted. He saw the way his roommate acted around his girlfriend, reserved and quiet, more than he usually was, and he even noticed the way Reiner’s eyes dipped down to your chest in the moment because Eren was exceptional at paying attention to detail.

You must have detected how uncomfortable Reiner felt because you delivered a brief jab to Eren’s ribs with your elbow.

“Eren, that’s not fucking funny,” you chided. “Do I need to put you in time out?”

“It’s fine,” Reiner interrupted quickly. He didn’t want you defending him because you were oblivious. It only made the situation more embarrassing than it already was since, truthfully, the thought had crossed his mind more than once.

Eren reiterated his question, eyes narrowed at Reiner. “So do you?”

You sighed heavily and looked at Reiner apologetically. He could feel his face growing hot, and he prayed it wasn’t obvious he was as flushed as he felt. He just wanted to get out of there as fast as possible.

Reiner released a humourless chuckle. “Grow up, Eren.” He slipped past the two of you, but he didn’t get far.

“I’m only asking because I’m feeling charitable. You wouldn’t mind, would you baby?”

Reiner could hear Eren pressing a series of ticklish kisses against your skin, causing you to laugh through your answer.

“I mean, I wouldn’t mind if Reiner doesn’t mind.”

Reiner brought his teeth down hard on the tip of his tongue. He was surprised that Eren was so secure in his relationship that he would willingly allow another man to have his way with his girlfriend. He wasn’t sure if his suggestion was insane or ingenious, because Eren had taken control of the one thing that threatened any relationship: _infidelity_ , something so unvirtuous wouldn’t stop him from loving you. You and Eren were so committed to each other that a simple fuck meant nothing.

Reiner hesitated, but figured an opportunity like this was rare. He had both Eren’s permission and yours, yet he still didn’t believe his sincerity until you were in Eren’s room, starting to strip out of your clothes.

His chestnut eyes drifted over to Eren, slouched lazily in the chair he casually pulled out from his desk. “You’re gonna watch?”

Eren lifted a thick eyebrow, resting his thumb under his chin with an index finger against his cheek, looking unimpressed by Reiner’s obvious reservations. “You think I’d let you fuck my girlfriend without me here?”

Reiner slid a tense hand over the back of his neck, rubbing away the uncomfortable heat that creeped up his back and diffused to the tips of his ears. He figured that was reasonable considering the circumstances, after all, he was only fucking you because Eren had allowed it.

There was nothing more intoxicating to Reiner than your bare form, scanty pink lace clinging to your hips the only thing preventing you from being completely naked in front of him. His gaze dipped from your simpering smile down to your collarbones and then down to your breasts, perfectly sculpted to your figure.

Reiner made no efforts to move despite his insatiable urge to grab you in his arms and make certain that you were left satisfied. He feared he’d look too eager to Eren who was observing from the sidelines, but you paid little attention to your audience of one as you sauntered towards Reiner, closer and closer, until your arms slid around his neck and you pressed your chest to his torso.

Reiner’s body was strung so tightly, he was afraid he might snap. It seemed you took notice of the way his muscles tensed once your delicate fingers ghosted over the nape of his neck because your suggestive expression waned, and instead, your eyebrows creased with sincere concern.

“You okay?”

He couldn’t respond, but to be fair, it was because his heart was hammering against his chest and he wasn’t sure how to make it stop. He looked over at Eren again, who, fortunately, didn’t seem to pay much attention to him. Instead, your boyfriend’s stare was fixed on your backside, likely admiring how luscious you looked from his perspective.

“I’m over here.” You laughed and pressed a gentle finger to Reiner’s chin, redirecting his focus back to you. “Just relax.”

He swallowed, chuckling to soothe his unease. “I’m trying.”

Reiner wasn’t sure why he felt so unassertive in your presence. He didn’t hold a record like Eren did, but he also wasn't abstinent by any means. This, though, felt different. He was dealing with several months of pent-up sexual frustration that could only be satisfied by you and no one else. He knew because he’d tried.

Reiner drew in a ragged breath as you leaned into him, breathing heavily through his mouth until you closed the space in between you two, then he continued breathing heavily through his nose. At first, he made no efforts to close his eyes, afraid that the imagery in front of him was a mirage inspired by his own imagination and would disappear if he so much as blinked. His lips were timid, body taut under your touch, but you seduced his mouth, reining him in until he melted into the kiss.

He pushed back against you with fervor and desperation, outlining the shape of your bottom lip with his tongue before nipping at the soft flesh. You released a quiet whimper, intensifying the lust swelling in the pit of his stomach, and Reiner forced his tongue past your teeth, claiming your mouth while his wandering hands settled audaciously against your ass.

Your hands slid over his shoulders and crafted biceps until they tugged hastily against the hem of his shirt, and Reiner immediately understood your cue, withdrawing his mouth from yours to give himself just enough time to slip out of it. He dipped down again to deliver another kiss, but he was deterred by the feeling of your palm against his chest.

“What? Is something wrong?” he questioned quickly, eyes darting back and forth between your hand and your face, worried that he’d done something to overstep your boundaries.

Instead of the troubled expression he expected, you looked rather intrigued. Perhaps impressed was the better word. Your curiosity was held by Reiner’s physique, a living work of art. Eager fingers traveled down the built ripples of his abdomen, chuckling once you felt his muscles flex under your touch.

“ _Jesus Christ_ ,” you breathed. “ _Nice_ , Braun.”

A snicker emitted from the corner. This, miraculously, Eren allowed.

Reiner's mouth quirked upward in a subtle smile before he surrounded you with his arm, pulling you in for another kiss. He walked you backwards until you collapsed onto the mattress, and he fell on top of you, strong forearms holding up his weight. It was then that Reiner realized he allowed his lust to win in the war against himself.

He pulled away to recover his breath, winded pants fanning over your face. His surveying eyes searched yours before they lowered to your swollen lips. _God_ , you were even more mesmerizing up close, heavy-lidded and studying him through a curtain of eyelashes. Maybe for once Reiner would admit he was jealous of Eren. He was fucking envious, bitter, and spiteful that you were his. He’d been a goddamn idiot to let things go this far, agreeing to Eren’s offer, because he knew one fuck wouldn’t be enough to fufill his need for you. He’d barely gotten a taste, and he could already promise that nothing would ever compare to this.

He found your throat and pressed a fleeting kiss to your pulse, moving further down until his lips met your collarbone. He nipped at the delicate skin, taking notice of the way your grip in his hair tightened. His eyebrows arched while he peered up at you, delighting in the way your head rolled back and forth against the duvet. He really wanted to suck at your skin, leaving dark bruises that decorated the path from your earlobe down to your breastbone, but he knew Eren would kill him.

Reiner dipped lower until his lips brushed lightly against your beaded nipple. You made a small sound of protest, but held his head closer, letting him know what you really wanted. His heart beat erratically against his ribcage as he curved a large hand around your right breast and suppressed a groan, but you released a breathy whimper.

He could feel the sound wreaking havoc in his brain. His balls were so damn tight, it would take barely any effort for him to cum, but he wanted to prolong your coupling as long as possible. He didn’t know if he’d ever get another chance like this. 

His thumb ran over the erect peaks of your breasts, captivated by the magic of watching your back arch and your body become aroused under his touch. He dipped a finger into his mouth, glazing it with his saliva before using it to flick back and forth at your nipple.

“ _Fuck, Reiner_ ,” you mewled.

Reiner replaced his hand with his lips, sucking the sensitive bud into his mouth. The tip of his tongue swirled around it, coating it generously with his spit, while you made no attempts to conceal your intense cries of pleasure. 

Eren released an entertained sigh, swiveling back and forth in his chair. “She whines like a bitch, doesn’t she?”

 _Shit._ Reiner had almost forgotten he was there, but he still released a hungry grunt in agreement, sending vibrations over your chest. He tugged at your nipple with his teeth, releasing it, and then soothing the sting with the flat side of his tongue.

He trailed down your abdomen, pressing hard wet kisses and stopping to leave a quick lick to your navel. He grinned against your skin when you gripped the sheets and breathed his name again, this time quieter, as if you meant it only for his ears. He liked to think so.

Once he reached the waistband of your panties, he licked along the fabric, immobilizing your rolling hips with strong hands.

“Enough with the theatrics, Reiner. Just do it already,” Eren groaned, sounding irate.

Reiner assumed Eren’s groan was only to stress his impatience, but once he looked over to him, he realized he wasn’t just giving directives from the sidelines. His bottom lip was tucked between his teeth, and his hand was moving steadily against the noticeable tent in his sweatpants.

He was enjoying this just as much as Reiner was, getting off to the sight of his girlfriend under another man, his roommate nonetheless.

Reiner suddenly felt strange. What the hell was _he_ doing providing entertainment for Eren?

“ _Reiner_ ,” your needy voice pulled him out of his reflection. His attention drifted back to you, watching while you propped yourself up on your elbows and slid your unsteady hands over your chest to tweak your own nipples, as if you were trying to hold yourself over.

He wished you hadn’t looked so tempting, even with your disheveled hair and sweaty skin, your vulnerable eyes fixated on him, and he was powerless.

Reiner hooked his fingers around your underwear, kissing a trail down the inside of your thighs as he pulled your panties down to your ankles before slipping them off and letting them pool on the floor.

“Spread wide baby, let him see that pretty pussy,” Eren stirred, cock now thrust out the top of his grey sweats and his swollen tip glistening with precum. His hand was wrapped firmly around his stiff length, moving slow while his breathing quickened.

For once, Reiner agreed with him, and he pressed his fingers into your thighs to aid you in parting your legs. Your pussy was slick with your own arousal, squelching as you tightened around nothing. You were even prettier than he’d imagined.

“ _Fuck_ ,” Reiner breathed, extending two fingers to part your folds. Was he still sure he wasn’t dreaming?

He wrapped his built arms around your legs, pulled you closer, and lowered his head. He fixed his lips to your swollen clit, allowing his tongue to lap and circle around the tender bud every few seconds.

“ _Oh my god_ ,” you cried, writhing against the sheets.

If he hadn’t secured your legs in his grip, he was certain you would have smothered him between your thighs out of reflex. He could detect the way you fought against his hold, but he far overpowered you in strength.

When he plunged his tongue inside you without notice, that was nearly enough to send you over the edge. You pulled on the sheets with a frenzied grip, producing a shrill cry your neighbors had certainly heard. There was no doubt about it.

“ _Fuck, fuck, fuck,_ ” you murmured, chest expanding and falling with labored breaths.

Reiner wanted to spend a few more generous minutes tasting you, he couldn’t get enough, but he also wasn’t sure how much longer he would last. His cock was hot and hard in his pants, and he needed to feel you around him. Even if Eren wouldn’t let him cum inside of you, he needed to experience at least that much.

He rose to his feet, working quickly against his pants’ zipper while trying not to tease himself by looking at you. He was worried the mere sight of you on the bed, spread and ready for him would be enough to bring him to a climax, but he’d made the mistake of looking at you anyways, hand between your legs, delicate fingers rubbing at your clit while you stared up at him.

 _Fucking hell. Kill me._ Reiner thought. _Fuck._ He felt the throbbing heat of his cock, and he wished you wouldn’t look at him like that. He really wished you wouldn’t look at him like _that_.

“Look at her, so desperate to be filled. It’s almost pathetic,” Eren laughed, but it was clear he was feeling your effect too. He lolled his head forward, long brown hair spilling over his shoulders and obscuring his face while his palm worked fast against his cock.

 _Shut up,_ Reiner thought. His head was growing hazy, and he couldn’t think. He needed to be inside you, and he couldn’t wait a second longer.

Reiner let himself free while his pants and underwear hung low around his knees. He couldn’t even find time to delight in the way your face melted into bliss once you laid eyes on his thick cock, leaking precum in sinful amounts because all he could think about was his ache. He leaned over you, positioning himself at your entrance.

He’d been waiting for this for so _goddamn_ long.

Reiner exhaled when you said his name again, hips undulating against his cock and wet folds stroking his tip. He watched as he pushed himself into you, filling you to the hilt, and once he was inside he hung his head forward, eyes shut tightly in a painful sort of ecstasy.

“You’re so _fucking tight_ ,” Reiner grunted breathlessly.

He groaned, pinning your hips down with his once you attempted to fuck yourself onto his cock.

“Stop moving,” he pleaded. “ _Jesus christ_ \--please _don’t move_.” He stayed still for a moment, waiting until his sensitivity subsided before he started rocking his hips against you slowly.

Reiner couldn’t dedicate his focus to anything other than the feeling of your slick walls clenching around his cock every time he pulled out, and the way he stretched you out every time he thrusted back in. He wondered if you could feel the depth of his desire.

“ _Harder,_ ” you whispered once, and then begged louder. “Reiner please, _fuck me harder._ ”

At first, Reiner was worried. He wanted to be gentle, he wanted to savor you, and he wanted to make sure he didn’t hurt you, but your request had him picking up the pace, ramming into you until the familiar slapping sound of sweaty skin filled the room. 

You unraveled and became completely undone, letting out loud moans every time he drove his cock into you. Reiner thought the sound was incredibly euphonic as it fell upon his ears. You were like this because of him.

“How’s this?” His voice was husky and deep beside your ear.

Reiner was pleased by your lack of response. You could only nod, overwhelmed by the dual sensation brought on by him and the feeling of your quick fingers against your clit. You secured an arm around his neck again and wrapped your legs around his torso, clinging to him like he was all you needed. He wished that was how you really felt.

“ _Close…_ ,” you murmured, and Reiner deduced you were warning him that you were near your orgasm. He could tell by the way your walls began to spasm.

Reiner felt the small of his back tighten, and he knew he was close too. He was torn between his release and holding himself back, not ready for this to end just yet, but his body betrayed him and he felt his cock twitch inside you.

Luckily, you reached your climax first, and Reiner watched in awe as your body seized underneath him, breasts bobbing with every jolt while you worked your clit into overstimulation. It wasn’t long after your orgasm that he made his last rueful thrusts. He quickly pulled out and clasped himself in the curve of his hand. He pumped his length until he released in quick spurts onto your stomach, covering you in his hot seed, and he kept pumping until he made sure he emptied himself of every drop.

His eyes quickly darted over to Eren, _not_ to be odd or anything, but again, he had forgotten he was there. It seemed Eren had already satisfied himself. The creamy, white liquid decorating the bare skin of his abdomen and dribbling down his loose fist was evidence of that. Now that he had appeased his urges, he seemed disinterested as he reached over his desk and plucked a few tissues to clean himself up.

Reiner collapsed beside you, listening to the loud thudding of his heart as it delivered a few ecstatic beats while he caught his breath and began to calm down. He stared at the pivoting fan blades, and then his eyes dropped down to you lying next to him, sweaty and fucked out.

You were laying there with _him_ , and goddammit he wanted to reach his arms out and wrap them around you, pulling you close so he could hold you and feel your heartbeat against his chest. He’d press kisses to your salty forehead, and then tell you how much he loved you. He wanted to stay like this.

Reiner's ideal vision dissolved once Eren stopped at the edge of the bed and extended his hand for you to grab.

“You wanna join me for a shower, baby?” Eren asked.

Of course, you took it, allowing him to support you until you were sitting up.

You released an exhausted laugh. “Yes, please.” You then turned to Reiner and arched your eyebrow in surprise. “By the way, not bad, Braun.”

Reiner gave you a small smile in return, but said nothing as he watched you cover your breasts with your arm and let Eren hoist you off the bed. You two slid past him and headed out of the room, but not without Eren looking back over his shoulder, shooting Reiner a shit-eating grin, as though reminding him who you’d always belong to.

**Author's Note:**

> as always thank you so much for reading and supporting! if you'd like, you can follow me on my tumblr by the same user piecksz! :)


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